2,9-dichloroquinacridone pigment

ABSTRACT

A new high chroma, opaque gamma 2,9-dichloroquinacridone pigment specified by its particle shape and size and characterized by C.I.E color space values in masstone, and a process for its preparation is dislosed. The new gamma 2,9-dichloroquinacridone pigment is especially useful for coloring coating compositions, such as automotive paints, and plastics.

This application is a continuation of International Application No.PCT/EP02/00728, filed Jan. 24, 2002, which claims the benefit of U.S.Provisional application No. 60/264,930, filed on Jan. 30, 2001.

The present invention relates to a 2,9-dichloroquinacridone pigment, inparticular to a novel form of a gamma 2,9-dichloroquinacridone pigmenthaving a distinguishing color characteristic, its preparation and itsuse as a pigment in high molecular weight organic materials.

Quinacridones, also referred to as5,12-dihydroquino[2,3-b]acridine-7,14-diones, are well-known highperformance organic pigments. In particular the linear2,9-dichloro-quinacridone of formula (I) is known for its outstandingpigment properties and its use as a magenta pigment.

Several patents describe the preparation and finishing of2,9-dichloroquinacridone, for example U.S. Pat. No. 3,157,659 describesthe preparation of alpha, beta and gamma 2,9-dichloroquinacridone in thepresence of sulfuric acid.

Additionally, U.S. Pat. No. 4,895,949 discloses a process for preparingpigmentary solid solutions of at least one quinacridone derivative andthe parent quinacridone by milling the starting quinacridone materialsat ambient or near ambient temperatures in the presence of an alcoholand a base.

DE-2,753,357 describes a conversion process of a preground2,9-dichloroquinacridone into a pigmentary form by contacting it with anaqueous alkaline medium at 85° C. in the presence of surfactant(s).

U.S. Pat. No. 5,194,088 describes a process for converting a crudeorganic pigment into a pigmentary form consisting essentially ofpremilling the crude pigment and contacting the premilled pigment with apolar organic solvent at a temperature below about 50° C.

A process for pigmenting engineering plastic substrates and coatingscomprising incorporating an effective pigmenting amount of2,9-dichloroquinacridone having a specific surface area of below 30 m²/ginto said engineering plastic or coating is described in the U.S. Pat.No. 5,095,056. The patent particularly emphasizes the increased heatstability of a larger particle size versus a smaller particle size2,9-dichloroquinacridone.

Indeed larger particle size 2,9-dichloroquinacridone pigments arecommercially available with a specific surface area of below 30 m²/ghaving excellent heat stability. however, at the cost of other pigmentproperties. In particular, their chroma and hiding power are still lowerthan desirable, and their hue is yellowish red. Such pigments have abroad pigment particle size distribution and an irregular particleshape. As shown by electron microscopy, the average aspect ratio oflength to width and/or height is at least 5:1, for example from 5:1 to15:1. The pigment particles show a great variety of shapes.

U.S. Pat. No. 5,084,573 discloses the conversion of a crude2,9-dichloro-quinacridone into a platelet form in a polar solvent in thepresence of an aliphatic long chain sulfur compound and a base.

Surprisingly, 2,9-dichloroquinacridone in its gamma crystal form with anessentially isometric to orthorhombic particle shape (short rod-likewith almost orthogonal axes and compact aspect ratio) with an averageparticle size in the range of 0.1 to 0.8 μm and a specific surface areain the range of 11 to 23 m²/g shows an unique magenta (bluish red) colorshade with surprisingly high chroma, extremely high opacity andexcellent weatherability behavior. Very thin, hiding layers of highgloss can be obtained for example in coatings. As shown by electronmicroscopy, the average aspect ratio of length to width and/or height isfrom 1:1 to 3:1.

High chroma and opacity are very desirable pigment properties, bothdesirable but most difficult to achieve simultaneously. Thus, the new2,9-dichloroquinacridone pigment is valuable since it offers the paintproducer new styling opportunities and the creation of very economic newcolor shades in particular in combination with other organic, inorganicor effect pigments. Hence, a difference in hue, chroma and opacity canbe of considerable commercial importance. Due to the outstandingfastness properties, its excellent rheological properties and uniquecolor characteristics, it is highly suited for use in plastics andcoatings applications, particularly in automotive coating systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an X-ray diffraction pattern of the inventiveγ-2,9-dichloroquinacridone pigment. The x-axis reflects the doubleglancing angles (°2θ) while the y-axis reflects the intensity of thediffracted ray.

FIG. 2 is an X-ray diffraction pattern of a premilled2,9-dichloroquinacridone that shows an alpha/gamma2,9-dichloroquinacridone mixture and a half band width of the peak at27.8 degree two theta angles of 1.2 to 1.5. The x-axis values are °2θ,while the y-axis values are expanded by a factor of 2.5, as comparedwith FIG. 1.

FIG. 3 is the electron micrograph of the 2,9-dichloroquinacridoneobtained according to Example 1C.

The present invention relates to a novel 2,9-dichloroquinacridonepigment which is specified by its crystal form, pigment particle sizeand shape, its specific surface area and its color characteristics. Thecolor space values are obtained by known measurements (as notedhereafter) from, for example, sprayed paint panels of a pigmentmasstone. A pigment masstone means that only one pigment is used tocolor the substrate. The color space values are defined using thehue-angle which is based on the L*C*h system of the CommissionInternationale de I'Éclairage (CIE) (DIN 5033 Part 3; DIN 6174). TheL*C*h system correlates with the 1976 CIE L*a*b* color space (hereinreferred as CIELab or CIELab-system).

The color space values of the gamma 2,9-dichloroquinacridone accordingto the present invention are characterized by the following values:

CIE color space broad in more most coordinates range particularpreferred preferred preferred L* (lightness) 35-42 35-42 36-42 36-4137-41 C* (chroma) ≧40 40-47 41-47 41-47 42-47 h (hue angle) 14-20 14-1915-19 15-18 16-18

The color measurements are carried out in a large area view with aspectral component using a ACS Colorimeter Program on an ACS, CS-5Chromasensor from Applied Color Systems, Inc. and distributed byDATACOLOR International.

In order to measure the color data, the pigment is first incorporatedinto a substrate, for example, an acrylic paint system such as thosedescribed in Example 5 or a polyester paint system such as described inexample 9. It is the color of the pigmented substrate such as the coatedpanel or a pigmented plastic sheet which is then measured. The color ismeasured at “complete hide”, which means that the substrate is pigmentedto such an extent that any background color is not observable. At“complete hide” it is not possible to see the background color of acoated panel or the background color through a pigmented plastic sheet(color measurements give identical results, for example with a black ora white panel as background). For practical purposes, it is sufficientto measure at incomplete hide on an acrylic or polyester enamel coating,provided the color difference ΔE* measured over a black and whitebackground is less or equal to 8, preferably ≦4.8, and to take theaverage value of over white and over black for each the lightness (L),the chroma (C*) and the hue angle (h). Optionally, a transparent clearcoat can be applied above the pigmented acrylic or polyester enamel sofar thin enough in order the color not to be altered.

Appropriate substrates include lacquers, inks, coating compositions, andplastics. Especially appropriate coating compositions include thebasecoat/clearcoat systems conventionally used in the automotiveindustry. Especially appropriate plastics include the polyvinyl halides,especially polyvinyl chloride, and the polyolefins, for example low orlinear low density or high density polyethylene, polypropylene,polyester, polyamide and ABS.

The new 2,9-dichloroquinacridone pigment shows a very high opacity for amagenta pigment. The opacity or hiding power is the capacity of acoating material to hide the color or differences in color of asubstrate. It is determined by comparative measurement of the reflectionof a coating material on a black and white substrate. Black and whiteglass plates or contrasting cards, for example, can be used as such asubstrate.

The instant 2,9-dichloroquinacridone pigment shows the typical X-raydiffraction pattern of gamma 2,9-dichloroquinacridone as depicted inFIG. 1.

Thus, the new gamma 2,9-dichloroquinacridone is characterized by anx-ray diffraction pattern having one strong peak corresponding to ±0.22θ double glancing angles of 27.8, five medium strength peakscorresponding to 5.2, 15.1, 16.4, 22.9 and 23.3, and seven relativelyweak peaks corresponding to 15.7, 19.2, 21.2, 24.4, 25.2, 26.5 and 28.9.For purposes of this application “strong” means having a relativeintensity above 60%, “medium” means between 20 and 60% and “weak” meansbelow 20% (see data in Example 1C).

A key feature of the instant gamma 2,9-dichloroquinacridone pigment isits narrow particle size distribution and its primary pigment particleshape of an essentially isometric to orthorhombic like shape with atleast 90% of the particles having a width of 0.1 to 0.4 μm and a lengthof 0.1 to 0.8 μm, and with at least 60% of the particles having a widthof 0.1 to 0.3 μm and a length of 0.1 to 0.6 μm as determined by anelectron micrograph. Primary particles can be single or sometimesagglomerated or grown together as twins.

Preferably, the pigment crystal is essentially isometric or tetragonalprovided it remains with the following ratios. The average aspect ratioof length to width and/or height is from 1:1 to 3:1; preferably, 1:1 to2:1; most preferably, 1:1 to 1.5:1. In other words, the ratio of thelonger dimension to the shorter dimension is less than 3:1,alternatively greater than 1:1 but less than 3:1. Still further, theratio of such dimensions is between 1:1 to 2:1. Preferably, at least 60%(more preferably 80% to 100%) of the primary particles fit into thisrange and have an almost rectangular outline (dihedral angle betweenopposite faces from 0° to about 20°, preferably from 0° to 10°, mostpreferred parallel, and dihedral angles between contiguous faces fromabout 70° to 90°, preferably from 80° to 90°, most preferredorthogonal).

The instant 2,9-dichloroquinacridone pigment shows a specific surfacearea of 11-23 m²/g, preferably 13-21 m²/g, most preferred 14-19 m²/g asdetermined by the BET method.

The instant 2,9-dichloroquinacridone also shows an outstanding viscositybehavior when incorporated in a paint system such as for example anautomotive paint system.

Additionally, panels sprayed with paints containing the instant2,9-dichloroquinacridone pigment do not show metamerism and maintain thehigh chroma magenta color when exposed to different light sources, suchas dim or sun or various sources of artificial light.

The instant gamma 2,9-dichloroquinacridone has superior pigmentproperties, such as a high opacity, excellent rheological properties,heat stability and weatherability behavior, as well as a remarkably goodflocculation resistance. It is easily dispersible and develops quickly ahigh color strength.

Although the instant pigment shows excellent application properties, inorder to further improve the pigment properties of the instant gamma2,9-dichloroquinacridone pigment, texture-improving agents and/oranti-flocculants optionally can be added before, during or after thecorresponding preparatory process.

The texture-improving agent and/or anti-flocculant is preferablyincorporated into the instant gamma quinacridone pigment in an amount offrom 0.05 to 20 percent, most preferably 1 to 10 percent, by weight,based on the combined weights of the gamma 2,9-dichloroquinacridonepigment, texture-improving agent and/or anti-flocculant mixture.

Texture-improving agents are especially useful as an additionalcomponent which improves the properties of the instant gamma2,9-dichloroquinacridone pigment. Suitable texture-improving agentsinclude fatty acids having at least 12 carbon atoms, and amides, estersor salts of fatty acids. Typical fatty acid derived texture-improvingagents include fatty acids such as stearic acid or behenic acid, andfatty amines such as laurylamine and stearylamine. In addition, fattyalcohols or ethoxylated fatty alcohols, polyols such as aliphatic1,2-diols, glycerol mono stearate or polyvinylalcohol and epoxidized soybean oil, waxes, resin acids and resin acid salts are suitabletexture-improving agents.

Anti-flocculants are known in the pigments industry and are often alsoused as rheology improving agents, for example, pigment derivatives suchas sulfonic acid, sulfonic acid salts like metal or quaternaryalkylammonium salts or sulfonamide derivatives. Generally,antiflocculants which are derivatives of a pigment from pigment classessuch as those described in U.S. Pat. No. 3,386,843 or U.S. Pat. No.4,310,359 are preferably utilized, which are incorporated herein byreference.

Due to its outstanding chemical resistance, heat stability, weather andlight stability, the instant gamma 2,9-dichloroquinacridone pigment ishighly suitable for the coloration of various substrates such asinorganic materials and in particular high molecular weight organicmaterials. Thus, the present invention relates to a method of coloring ahigh molecular weight organic material which comprises incorporating aneffective pigmenting amount of the instant pigment into the highmolecular weight organic material and to a composition comprising a highmolecular weight organic material and an effective pigmenting amount ofthe instant gamma 2,9-dichloroquinacridone pigment.

An effective pigmenting amount is any amount suitable to provide thedesired color in the high molecular weight organic material. Inparticular, the instant gamma 2,9-dichloroquinacridone pigment is usedin an amount of 0.01 to 30% by weight, preferably 0.1 to 10% by weight,based on the weight of the high molecular weight organic material to bepigmented.

The pigmented, high molecular weight organic materials which are coloredwith the instant pigment are useful in a variety of applications. Forexample, the instant pigment is useful for the pigmentation of lacquers,inks, enamel coating compositions and thermoplastic or thermosetpolymers.

The high molecular weight organic materials which are colored with theinstant pigment generally have a molecular weight in the range of from10³ to 10⁸ g/mol and are, for example, cellulose ethers, celluloseesters, polyurethanes, polyesters, polycarbonates, polyolefins,polystyrene, polysulfones, polyamides, polycycloamides, polyimides,polyethers, polyether ketones, polyvinyl halides,polytetrafluoroethylene, acrylic and methacrylic polymers, rubber,silicone polymers, phenol/formaldehyde resins, melamine/formaldehyderesins, urea/formaldehyde resins, epoxy resins and diene rubbers orcopolymers thereof.

High molecular weight organic materials which are useful forheat-curable coatings or cross-linked, chemically-reactive coatings, arealso colored with the instant pigment. The pigmented, high molecularweight organic materials prepared according to the present invention areespecially useful in finishes which contain customary binders and whichare reactive at high temperature. These finishes can be obtained fromsolvent or aqueous or powder paint systems known in the art. Examples ofpigmented, high molecular weight organic materials which are used incoatings include acrylic, alkyd, epoxy, phenolic, melamine, urea,polyester, polyurethane, blocked isocyanate, benzoguanamine or celluloseester resins, or combinations thereof. The pigmented, high molecularweight organic materials prepared according to the present invention arealso useful as air-drying or physically-drying coatings for example incosmetics use.

The instant gamma 2,9-dichloroquinacridone pigment is particularlysuitable for preparing aqueous and solvent based coatings conventionallyemployed in the automobile industry, especially in acrylic/melamineresin, alkyd/melamine resin or thermoplastic acrylic resin systems, aswell as in powder coatings and UV/EB cured coating systems.

Coatings and ink systems colored with the instant gamma2,9-dichloroquinacridone pigment possess a high gloss, a high opacity,excellent heat, light and weather fastness, as well as bleed andoverspraying fastness properties.

The instant pigment is prepared from 2,9-dichloroquinacridone crude,according to a process the key of which is the pigment crude producedand a finishing step. Suitable finishing processes start from2,9-dichloroquinacridone obtained by direct pigmentary procedures inwhich, for example, 2,9-dichloro-6,13-dihydroquinacridone is oxidized to2,9-dichloroquinacridone pigment in the presence of a catalyst withhydrogen peroxide as oxidant and optionally in the presence of a pigmentparticle growth and particle phase director.

The 2,9-dichloroquinacridone crude can have any crystal modification ora mixture of crystal modifications such as the known alpha, beta orgamma form, preferably it has a gamma or alpha crystal form or a mixturethereof. The 2,9-dichloroquinacridone crude is premilled optionally inthe presence of an inorganic salt such as sodium sulfate, calciumchloride or sodium chloride. In a preferred procedure, the pigment crudeis premilled in the presence of 10-30% inorganic salt such as NaCl,CaCl₂, Na₂SO₄ or Al₂(SO₄)₃ with or without water of hydration. Thepreferred milling mixture composition is 75 to 85% pigment crude and15-25% anhydrous Na₂SO₄.

Premilling, as the term is used herein, refers to milling in thecomplete absence of liquids, or if liquids are used such as a phasedirecting solvent or a surface active agent, they are present in suchsmall amounts (maximum of about 10% by weight of pigment) or of such anature that the mill charge retains the characteristics of a powder anddoes not in the following solvent treatment step affect the conversionto the instant gamma 2,9-dichloroquinacridone.

The premilling of the 2,9-dichloroquinacridone crude of the abovefinishing procedure is carried out for example in a horizontal or avertical bead mill such as an attritor or ball mill or in a high speedmixer known in the industry. The optional presence of an inorganic saltcan act as a grinding aid and increase the ability to flow and thereforeincrease the discharge amount of the resulting premilled powder.

Premilling operations are known and can be accomplished in various ways.Thus, it is possible to premill with 12.7 mm steel balls and roofingnails, or to avoid metal attrition and the corresponding need forpigment extraction with dilute acid, premilling can be accomplished with12.7 mm high density, high alumina ceramic balls or rods (DiamoniteProducts Manufacturing, Inc.). Ceramic beads of 0.1 to 2.5 cm,preferably 0.5 to 1.0 cm size made from crystalline zirconia phase andamorphous silica phase by fusion of the oxides are particularly suitable(product of Quartz Products Corporation). Although a variety of sizes ofgrinding media can be used, the aforementioned sizes are preferred.Grinding apparatuses are known, a ball mill, or an attritor mill filledwith metal or porcelain balls, preferably ceramic beads, being suitable.

The resulting premilled powder is highly aggregated and of lowcrystallinity as shown by the broad peaks of the x-ray diffractionpattern. The premilled powder is specified by the measurements of thehalf band width of the 27.8 degree two theta angle, which is preferablyin the range of 1.0 to 1.5, more preferably 1.2 to 1.5.

Then, the premilled 2,9-dichloroquinacridone is subjected to anaftertreatment in a polar organic solvent. Surprisingly, the premilled2,9-dichloroquinacridone can be converted to the instant gamma2,9-dichloroquinacridone only by selected polar solvents, such asdi(N—C₁-C₈-alkyl, preferably methyl)acetamide, formamide, methylacetamide, methyl formamide, di(C₁-C₈-alky)sulfoxide, sulfolanne,di(N—C₁-C₈-alkyl)formamide and N—C₁-C₈-alkyl-pyrrolidone; mostpreferably, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF) orN-methyl-pyrrolidone (NMP). The skilled artisan will also consider otherpolar organic solvents chosen amongst such having an oxo group and adipole moment μ of from about 2.8 to about 6.0 Debye units(2.8-6.0·10⁻¹⁸ esu, measured in benzene at 25° C.), preferably from 3.8to 5.0 Debye units (3.8-5.0·10⁻¹⁸ esu) and to solvatize. Alternativesolvents to be considered should preferably be hydrophilic, mostpreferably mixable with water in any proportions, such astetramethylurea.

The premilled pigment or pigment salt mixture is first separated fromthe grinding media, for example, by sieving and is then suspended in ahighly polar solvent, together with the inorganic salt used as agrinding help if applicable.

The after treatment step in the polar solvent is carried out in anysuitable equipment, such as a kneader or preferably a vessel with astirrer, to ensure complete contact between solvent and pigmentparticles. Preferably the suspension is stirred at a temperature above60° C. up to 240° C., and most preferably at 100 to 200° C. for 5minutes to 20 hours, preferably 30 minutes to 5 hours, depending on thedesired pigmentary properties of the ultimate product. The highly polarsolvent is generally present in an amount ranging from 5 to 20 times theweight of pigment, and preferably 8 to 15 times. The ripening processmay be conducted under any pressure (for example from 10⁴ to 10⁶ Pa,optionally in an inert atmosphere, provided the polar solvent is liquidand stable under the ripening conditions.

Contact of the premilled powder with the solvent causes the aggregatedpigment powder to deaggregate and undergo particle ripening. Ripening(recrystallisation) is a process in which the particles take the desiredshape and size while they are if necessary converted from a partiallyamorphous state or from an undesired crystal modification to a highlycrystalline gamma phase. Owing to the high temperature at which thesolvent treatment is conducted, the ripening process can be easilycontrolled as a function of time.

Advantageously, the instant process does not require the presence of anyadditives, such as phase directors, growth inhibitors, dispersants orthe like, though adding such compounds in customary amounts would ofcourse be feasible. On the contrary, it has been found that betterresults are obtained in the complete absence of additives.

Another aspect to be considered when preparing the instant gamma2,9-dichloroquinacridone is the purity of the 2,9-dichloroquinacridonecrude to be used. It has surprisingly been found that the higher thepurity, the better (more isometric) aspect ratio is obtained. Thus, itis suitable to use a 2,9-dichloroquinacridone crude of high purity—thatis, one that contains little of the starting materials, for example the2,9-dichloro-6,13-dihydroquinacridone or other by-products such as the2,9-dichloroquinacridone quinone or others generated during thequinacridone synthesis, including synthesis by other than oxidation withhydrogen peroxide.

The high purity 2,9-dichloroquinacridone crude preferably has a purityof at least 97%, most preferably of above 97.5% as measured by aspectroscopic method in which the 2,9-dichloroquinacridone is dissolvedin concentrated sulfuric acid. Advantageously, a high purity2,9-dichloroquinacridone crude is prepared by the oxidation of the6,13-dihydroquinacridone in the presence of an oxidation promotingcatalyst, such as quinone compounds, with hydrogen peroxide as theoxidant as described in the U.S. Pat. No. 5,840,901, which isincorporated herein by reference.

Since the ultimate pigment particle size is generated during the solventtreatment, the pigment can be isolated directly by filtration, washingthe presscake with water and/or organic solvents such as alcohols likemethanol, ethanol, n-propanol or isopropanol, and drying.

In comparison to commercially available magenta pigments, such as opaquebeta quinacridone or other commercially available large particle size2,9-dichloroquinacridone pigments, the innovative2,9-dichloroquinacridone exhibits a uniquely high chroma magenta colorwith a high opacity and outstanding pigment properties.

The instant 2,9-dichloroquinacridone pigments show an extremely highopacity of from ΔE (less than or equal to) ≦8, preferably ≦4.8 and mostpreferably ≦4.0 suitably measured at in a 25±5 μm thick acrylic orpolyester enamel coating system having a pigment to binder weight ratioof 0.18 over a black and white background and prepared and measuredaccording to established industry procedures. Such opacity is notreached by any previous 2,9-dichloroquinacridone magenta pigments.

The following examples illustrate various embodiments of the invention,but the scope of the invention is not limited thereto. In the examples,all parts are by weight unless otherwise indicated. The x-raydiffraction patterns are measured on a RIGAKU GEIGERFLEX diffractometer,type D/MaxII v BX. The coloristic data are obtained utilizing a CS-5CHROMA SENSOR spectrophotometer as described above and the electronmicrograph was taken on a Zeiss type 910 electron microscope.

EXAMPLE 1A

A 2,9-dichloroquinacridone crude with a specific surface area of 7.2m²/g and a purity of 97.8% 2,9-dichloroquinacridone as determinedspectrophotometrically, and which is obtained by the oxidation of2,9-dichloro-6,13-dihydroquinacridone with hydrogen peroxide as theoxidant as described in U.S. Pat. No. 5,840,901 is premilled accordingto the following procedure:

A 1-SDG Attritor™ mill manufactured by Union Process, Inc. Akron, Ohio,fitted with L-arms and containing 3.78 liters of 0.6 cm diameter ceramicgrinding media with 7.5 MOH hardness, 60-65 Rockwell 45 N hardness, 3.0kg/cm impact strength and 8500 kg/cm compressive strength, is chargedwith 500 grams of the 2,9-dichloroquinacridone crude and the pigment ismilled under a nitrogen flow at a rotation speed of 500 rpm for 60minutes. At the conclusion of the milling cycle, the product isrecovered by opening the valve at the bottom of the mill while rotationcontinues for 15 minutes yielding a brown highly aggregated powder witha low crystallinity.

EXAMPLE 1B

The procedure of Example 1A is repeated but charging the attritor withan additional amount of 75 grams anhydrous sodium sulfate yielding anhomogenous brown highly aggregated powder with a low crystallinity, andwhich can be easily discharged in a high yield.

EXAMPLE 1C

A one liter flask equipped with a thermometer, stirrer and condenser ischarged with 500 ml NMP and stirred at room temperature (20-27° C.).Fifty-five grams premilled 2,9-dichloroquinacridone powder according toExample 1A are slowly added. The suspension is thin and easilystirrable. Additional 50 ml NMP are added to rinse the funnel and thesuspension is heated in 30 minutes to 150-153° C. and stirred at thattemperature for 3 hours. The suspension is then stirred without heatingfor 30 minutes, allowing the temperature to decrease to 60-65° C., andit is finally filtered. The press cake is washed with methanol followedby water and dried yielding a high chroma, highly opaque magenta pigmentwhich after pulverization can be employed in paints, inks and plastics.

The electron micrograph shows pigment particles with an isometric ororthorhombic shape (short rod-like with almost orthogonal axes) and withat least 90% of the particles keeping a width of 0.1-0.4 μm and a lengthof 0.1-0.8 μm as shown in FIG. 3.

The x-ray diffraction pattern shows the characteristic pattern of agamma 2,9-dichloroquinacridone (FIG. 1) with the following data:

SCATTERING RELATIVE ANGLE [°2θ] INTENSITY [%] 5.2 22 15.1 41 15.7 8 16.422 19.2 16 21.2 7 22.9 25 23.3 34 24.4 11 25.2 10 26.5 13 27.8 100 28.910

EXAMPLE 2

The procedure of Example 1C is repeated, using instead of NMP the sameamount of dimethyl sulfoxide (DMSO) as the polar solvent, yielding agamma 2,9-dichloroquinacridone with a similar color characteristic andsimilar good pigment properties.

EXAMPLE 3

The procedure of Example 1C is repeated, using the same amount ofpremilled 2,9-dichloroquinacridone powder according to Example 1Binstead of premilled 2,9-dichloroquinacridone powder according toExample 1A, the same amount of dimethylformamide (DMF) as the polarsolvent instead of NMP, and stirring the suspension at refluxtemperature for 4 hours, yielding a gamma 2,9-dichloroquinacridone witha similar color characteristics and similar good pigment properties.

EXAMPLE 4

The procedure of Example 1C is repeated; however stirring the suspensionfor 3 hours at reflux, instead of stirring for 3 hours at 150 to 153°C., yielding a high chroma gamma 2,9-dichloroquinacridone magentapigment having a slightly yellower shade versus the pigment preparedaccording to Example 1C but with similar good pigment properties.

EXAMPLE 5

This Example illustrates the incorporation of the instant gamma2,9-dichloroquinacridone prepared according to Example 1C into anautomotive paint system.

Millbase formulation: A pint jar (473.18 ml) is charged with 48 gramshigh solids acrylic copolymer polyol resin (68% solids, DU PONT), 10.5grams acrylic A-B dispersant resin (55% solids, DU PONT) and 42.3 gramsSolvesso 100 (American Chemical). 19.2 grams gamma2,9-dichloroquinacridone obtained according to Example 1C and 240 gramsof glass beads are added. The mixture in the jar is shaken on a Skandexshaker for 1 hour. The millbase contains 16.0% pigment with apigment/binder ratio of 0.5 and a solids content of 48%.

Masstone color for spraying a panel: 43.7 grams of the above millbase,25.4 grams of an unpigmented commercial automotive basecoat (blend ofpolyester/polyol resin, acrylic copolymer polyol resins, melamine resin,additives and solvent 47.8% solids, DU PONT), 17.3 grams of a melamineresin Cymel 327 (Cyanamid) and 14.0 grams of a commercial unpigmentedautomotive basecoat consisting of a blend of polyester/polyol, acryliccopolymer polyol and melamine resins, additives and solvent (58% solids,DU PONT) are mixed and diluted with a solvent mixture comprising 76parts xylene, 21 parts butanol and 3 parts methanol to a spray viscosityof 20-22 seconds as measured by a #2 Fisher Cup.

The resin/pigment dispersion is sprayed onto a panel twice at 1½ minuteintervals as basecoat. After 2 minutes, the clearcoat resin is sprayedtwice at 1½ minute intervals onto the basecoat. The sprayed panel isthen flashed with air in a flash cabinet for 10 minutes and then “baked”in an oven at 129° C. (265° F.) for 30 minutes, yielding a magentacolored panel. The coated panel has excellent weatherability as shown bythe exposure data in an ATLAS weather-O-meter.

The following C.I.E. L*, C*, h color space values are measured on thecoated panel using a D65 illuminant and 10 degree observer with aspecular component included:L*=37.5; C*=43.1; h=16.6.

Masstone color for an acrylic enamel drawdown: 47.3 grams of the abovemillbase, 36.4 grams of acrylic A-B dispersant resin (55% solids, DUPONT), 16.3 grams of an high solids acrylic copolymer polyol resin (68%solids, DU PONT) are mixed, yielding a resin/pigment dispersion with aconcentration of 7.6% pigment in a pigment to binder ratio of 0.18 and asolid content of 49.7%.

The resin/pigment dispersion is drawn down onto a Leneta black and whitechart from the Leneta Company using a 100 μm wet film applicator. Thefilm is flashed in a flash cabinet for 15 minutes and baked for 10minutes. The final thickness of the coating is 25 μm.

The following ΔE* number is measured over the black and whitebackground: ΔE*=4.0. The hide is almost complete as seen with the nakedeye.

The C.I.E. L*, C*, h color space values are obtained from the portionover white background using a D65 illuminant and 10 degree observer witha specular component included:L*=36.7; C*=43.0; h=16.6.

EXAMPLE 6

63.0 grams of polyvinyl chloride, 3.0 grams epoxidized soy bean oil, 2.0grams of barium/cadmium heat stabilizer, 32.0 grams dioctyl phthalateand 1.0 gram of the gamma 2,9-dichloroquinacridone pigment preparedaccording to Example 1C or 2 to 4 are mixed together in a glass beakerusing a stirring rod. The mixture is formed into a soft PVC sheet with athickness of about 0.4 mm by rolling for 8 minutes on a two rolllaboratory mill at a temperature of 160° C., a roller speed of 25 rpmand friction of 1:1.2, by constant folding, removal and feeding. Theresulting soft PVC sheet is colored in an attractive magenta shade andhas excellent fastness to heat, light and migration.

EXAMPLE 7

Five grams of the gamma 2,9-dichloroquinacridone pigment preparedaccording to Example 1C, 2.65 grams ®CHIMASORB 944LD (hindered aminelight stabilizer), 1.0 gram ®TINUVIN 328 (benzotriazole UV absorber) and2.0 grams ®IRGANOX B-215 Blend (anti-oxidant), all available from CibaSpecialty Chemicals Corporation, are mixed together with 1000 grams ofhigh density polyethylene at a speed of 175-200 rpm for 30 seconds afterflux. The fluxed, pigmented resin is chopped up while warm andmalleable, and then fed through a granulator. The resulting granules aremolded on an injection molder with a 5 minute dwell time and a 30 secondcycle time at a temperature of 200, 250 and 300° C. Homogeneouslycolored chips which show a saturated reddish magenta color withpractically no color differences are obtained. They have an excellentlight stability.

The following C.I.E. L*, C*, h color space values are obtained on a chipmolded at 200° C. using a D65 illuminant and 10 degree observer with aspecular component included:L*=40.5; C*=46.1; h=17.5.

EXAMPLE 8

1000 grams of polypropylene granules (DAPLEN PT-55® from Chemie Linz)and 10 grams of the gamma 2,9-dichloroquinacridone pigment obtained inExample 1C or 2-4 are thoroughly mixed in a mixing drum. The granules soobtained are melt spun at 260-285° C. to red filaments of good lightfastness and textile fiber properties.

EXAMPLE 9

This Example illustrates the incorporation of the instant gamma2,9-dichloroquinacridone prepared according to Example 1C into anautomotive polyester/CAB enamel paint system.

Binder Solution (8.2% Binder):

-   41.0 CAB® 531.1 (Eastman Chem.), 20% in butyl acetate/xylene 2:1-   1.5 NUODEX® 6 (zirkonium octoate, Nordmann, Rassmann, D-Hamburg)-   18.5 Solvesso® 150 (Exxon)-   21.5 butyl acetate-   17.5 xylene

Millbase formulation: A 250 ml jar is charged with 15.73 grams Dynapol®H 700-08 (Degussa-Hüls), 11.80 grams of the above freshly preparedbinder solution, 11.80 grams Maprenal® MF 650 (Vianova Resins) and 2.67grams dispersant Disperbyk® 161 (BYK Chemie). 8 grams gamma2,9-dichloroquinacridone obtained according to Example 1C and 100 gramsof glass beads are added. The mixture in the jar is shaken on a Skandexshaker for 1 hour. The millbase contains 16.0% pigment with apigment/binder ratio of 1:2.25 and a solids (pigment+binder) content of59%.

Masstone color for an PES/CAB enamel drawdown: 23.75 grams of the abovemillbase, 10.50 grams of Dynapol H 700-08, 7.87 grams of the abovebinder solution and 7.87 grams Maprenal MF 650 are mixed, yielding aresin/pigment dispersion with a concentration of 7.6% pigment in apigment to binder ratio of 1:5.22 and a solid (pigment+binder) contentof 47.3%.

The resin/pigment dispersion is drawn down onto a Leneta black and whitechart from the Leneta Company using a 100 μm wet film applicator. Thefilm is flashed in a flash cabinet for 30 minutes and then “baked” in anoven at 130° C. (266° F.) for 30 minutes. The final thickness of thecoating is 28 μm.

The following ΔE* number is measured over the black and whitebackground: ΔE*=5.4. This coloristic difference corresponds to asatisfactory hide.

The C.I.E. L*, C*, h color space values are obtained from the portionover white background using a D65 illuminant and 10 degree observer witha specular component included:L*=38.2; C*=43.9; h=16.6.

Further examples: Of course, it is possible to vary the pigmentconcentration and the layer thickness. By increasing the pigmentconcentration for example to 10%, 15% or 20% by weight, it is possibleto obtain a good hide already with thinner layers, for example only 20μm, 15 μm or even 10 μm thick. This is only possible owing to theinstant pigments' excellent rheology. The skilled artisan will easilyfully appreciate all hitherto unworkable possibilities that the instantpigments enable him to reach.

1. A gamma 2,9-dichloroquinacridone pigment having particles with aspecific surface area of 11-23 m²/g, which pigment comprises C.I.E.color space values in masstone of L*=35-42, C* is at least 40 andh=14-20, measured on a panel coated with an acrylic or polyester enamelcoating of dry film thickness of 25±5 μm and pigment to binder weightratio of 0.18 over a black and white background, which enamel coatinghaving such opacity that a color difference ΔE* over the black and overthe white background is less than or equal to
 8. 2. A gamma2,9-dichloroquinacridone pigment according to claim 1 comprising atleast 90% of the primary particles with an average particle size in therange of 0.1 to 0.8 μm, wherein at least 60% of said particles have anaverage aspect ratio of length to width and/or height from 1:1 to 3:1.3. A gamma 2,9-dichloroquinacridone pigment according to claim 1, whichis characterized by C.I.E. color space values in masstone of L*=37-41,C*=42-47 and h=16-18.
 4. A composition comprising a high molecularweight organic material in the range of 10³ to 10⁸ g/mol and aneffective pigmenting amount of a gamma 2,9-dichloroquinacridone pigmentaccording to claim
 1. 5. A composition according to claim 4, whereinsaid high molecular weight organic material is selected from the groupconsisting of cellulose ethers, cellulose esters, polyurethanes,polyesters, polycarbonates, polyolefins, polystyrene, polysulfones,polyamides, polycycloamides, polyimides, polyethers, polyether ketones,polyvinyl halides, polytetrafluoroethylene, acrylic and methacrylicpolymers, rubber, silicone polymers, phenol/formaldehyde resins,melamine, formaldehyde resins, urea/formaldehyde resins, epoxy resins,diene rubbers and copolymers thereof.
 6. A composition according toclaim 4, wherein said high molecular weight organic material is aplastic that is subsequently calendered, cast, molded or processed tofibers, or is an industrial or automotive paint or ink coating.
 7. Aprocess for coloring a high molecular weight organic material in therange of 10³ to 10⁸ g/mol, which comprises incorporating an effectivepigmenting amount of a pigment according to claim 1 into the highmolecular weight organic material.
 8. A gamma 2,9-dichloroquinacridonepigment having primary particles comprising at least 90% of said primaryparticles with an average particle size in the range of 0.1 to 0.8 μm,wherein at least 60% of said particles have an average aspect ratio oflength to width and/or height from 1:1 to 3:1.
 9. A gamma2,9-dichloroquinacridone pigment according to claim 8, wherein at least60% of the primary particles have a length in the range of 0.1 to 0.8 μmand a shape with dihedral angle between opposite faces from 0° to about20° and dihedral angles between contiguous faces from about 70° to 90°.10. A gamma 2,9-dichloroquinacridone pigment according to claim 8,having a specific surface area of 11-23 m²/g.
 11. A gamma2,9-dichloroquinacridone pigment according to claim 8, which ischaracterized by C.I.E. color space values in masstone of L*=37-41,C*=42-47 and h=16-18.
 12. A gamma 2,9-dichloroquinacridone pigmentaccording to claim 9 having a specific surface area of 11-23 m²/g.
 13. Aprocess for the preparation of a gamma 2,9-dichloro-quinacridonepigment, comprising a) oxidizing a 2,9-dichloro-6,13-dihydroquinacridonewith hydrogen peroxide to produce a 2,9-dichloro-quinacridone crudeproduct; b) grinding the resulting 2,9-dichloroquinacridone crudeproduct to form a premilled 2,9-dichloroquinacridone product; c)contacting the premilled 2,9-dichloroquinacridone product with a polarsolvent; d) heating the premilled 2,9-dichloroquinacridone product andsolvent mixture at a temperature greater than 60° C. to ripen thepremilled 2,9-dichloroquinacridone product; and e) isolating the ripened2,9-dichloroquinacridone pigment having particles with a specificsurface area of 11-23 m²/g, which pigment is characterized by C.I.E.color space values in masstone of L*=35-42, C* at least 40 and h=14-20,measured on a panel coated with an acrylic or polyester enamel coatingof dry film thickness of 25±5 μm and pigment to binder weight ratio of0.18 over a black and a white background, which enamel coating has suchopacity that the color difference ΔE* over the black and over the whitebackground is less than or equal to 4.8.
 14. A process according toclaim 13, wherein said ripened pigment is characterized by C.I.E. colorspace values in masstone of L*=37-41, C*=42-47 and h=16-18.
 15. Aprocess according to claim 13, wherein the polar solvent is methylacetamide, formamide, sulfolane, methyl formamide,di(C₁-C₈-alkyl)sulfoxide, (N,N—C₁-C₈-alkyl)-formamide orN—C₁-C₈-alkyl-pyrrolidone.
 16. A process for coloring a high molecularweight organic material in the range of 10³ to 10⁸ g/mol, whichcomprises incorporating an effective pigmenting amount of a pigmentprepared according to claim 13 into a high molecular weight organicmaterial.
 17. A process according to claim 15, wherein the polar solventis dimethyl sulfoxide, dimethyl formamide or N-methyl-pyrrolidone.
 18. Aprocess for the preparation of a gamma 2,9-dichloro-quinacridonepigment, comprising a) oxidizing a 2,9-dichloro-6,13-dihydroquinacridonewith hydrogen peroxide to produce a 2,9-dichloro-quinacridone crudeproduct; b) grinding the resulting 2,9-dichloroquinacridone crudeproduct to form a premilled 2,9-dichloroquinacridone product; c)contacting the premilled 2,9-dichloroquinacridone product with a polarsolvent; d) heating the premilled 2,9-dichloroquinacridone product andsolvent mixture at a temperature greater than 60° C. to ripen thepremilled 2,9-dichloroquinacridone product; and e) isolating the ripened2,9-dichloroquinacridone pigment having primary particles comprising atleast 60% of said primary particles with an average particle size in therange of 0.1 to 0.8 μm, wherein the average aspect ratio of length towidth and/or height is from 1:1 to 3:1.
 19. A process according to claim18, wherein said ripened pigment is characterized by C.I.E. color spacevalues in masstone of L*=37-41, C*=42-47 and h=16-18.
 20. A processaccording to claim 18, wherein the polar solvent is methyl acetamide,formamide, sulfolane, methyl formamide, di(C₁-C₈-alkyl)sulfoxide,(N,N—C₁-C₈-alkyl)-formamide or N—C₁-C₈-alkyl-pyrrolidone.
 21. A processaccording to claim 20, wherein the polar solvent is dimethyl sulfoxide,dimethyl formamide or N-methyl-pyrrolidone.
 22. A process for coloring ahigh molecular weight organic material in the range of 10³ to 10⁸ g/mol,which comprises incorporating an effective pigmenting amount of apigment prepared according to claim 18 into a high molecular weightorganic material.